A majority of the chemical reactions demand the configuration of the reactor system such as to provide high rate of production, selectivity towards the desired product, and negligible production of intermediate products and byproducts. Multi-phase reactor systems are specially designed for performing gas-liquid or gas-liquid-solid reactions. These reactor systems typically comprise a reaction vessel including baffles and agitation devices such as impellers, and are therefore commonly referred to as “stirred tank reactors” or “STR”. Often, the reaction vessels also include gas spargers to disperse a gas into a bulk liquid medium. These multi-phase reactor systems are commonly used in fermentation, hydrogenation, phosgenation, neutralization, chlorination and oxidation reactions, where it is necessary to make intimate contact between the liquid and gas phase constituents to achieve the desired yield and production rate. Further, the reliable operation of these systems largely depends upon proper flow distribution and fluid dynamic behavior.
The configuration and geometry of the reaction vessel, impellers and gas spargers is mainly governed by the degree of homogeneity, required rate of mass transfer, solid suspension, and power consumption. Sometimes the nature of the chemical reaction demands auxiliary equipment or vessel internals like vessel jacket, internal heating or cooling coils and slinger devices.
Generally, in the gas-liquid or gas-liquid-solid reactions, gas is sparged at the bottom of the reaction vessel and feed is charged from the vessel top or middle. The unreacted gas leaves from the top liquid surface into an overhead system. This gas generally carries liquid droplets to the overhead system which causes fouling and corrosion in the overhead system. In exothermic reaction process, the heat of the reaction continuously boils the reactor liquid or the reaction medium which gets vaporized to maintain the required reaction temperature. These vapors also carry liquid droplets to the overhead system. In three-phase reactions, suspended solids from the reaction medium are also carried over by these vapors or unreacted gas to the overhead system causing solid built-up in the overhead system and solid deposition on the inner wall of the vessel headspace. Under these circumstances slinger devices are provided. In the known multi-phase reactor systems, a slinger device is provided near the operative top of the reaction vessel, typically on the agitator shaft of the reaction vessel, to spray a recycle liquid and/or fresh liquid over the free liquid surface of the reaction vessel and the vessel inner wall. The spraying of the liquid reduces both wall fouling and condenser plugging by washing the inner wall of the reaction vessel and scrubbing the gas leaving the reaction vessel.
An example of such multi-phase reaction is the oxidation of aromatic alkyls (e.g. p-xylene) within a liquid phase reaction medium, for e.g. the process of manufacturing terephthalic acid from p-xylene. In this process air is sparged through nozzles provided near the tip of the axial flow impellers in a reaction medium of solvent, catalyst, initiators and p-xylene. Heat generated by the exothermic oxidation reaction is dissipated by the vaporization of the solvent and the water produced by the oxidation of p-xylene. The temperature in the reaction vessel is controlled by the vaporization of the solvent and water and by recycle of the condensate stream of the overhead vapors. Crude terephthalic acid is recovered from the reaction product by crystallization and filtration.
Most of the terephthalic acid crystals is suspended within the liquid phase and can build-up on the walls of the reaction vessel. This causes reduction in the operating volume of the reactor, decreases the residence time of the reaction, and results in the formation of intermediate byproduct. Vaporization of the solvent from the reaction vessel can also carry fine solid particles to the overhead condenser system which leads to plugging of the overhead condenser tubes. The uneven heating and cooling of the reaction vessel wall also causes a thermal stresses at the vessel shell and can lead to shell leak. In such continuous boiling oxidation reaction vessel of a terephthalic acid manufacturing plant, condensate stream of the overhead vapors is fed back to the reaction vessel through a top and bottom reflux line. The objective of top reflux is to wash the reaction vessel wall to avoid any solid deposition and scrub the vapors containing solid particles entering into the overhead condenser system. The objective of the bottom reflux is to increase the conversion of p-xylene to terephthalic acid and reduce the acetic acid burning by reducing the severity of reaction vessel.
However, the conventional slinger devices consist of rotating, flat circular disks comprising multiple vertically raised straight vanes extending radially outward from a center hub of the disc to its outer periphery. The condensate is returned to the reaction vessel via a conduit located above the slinger device. The condensate is fed onto the slinger device from where it is subsequently distributed radially outward about the reaction vessel. These slinger devices, which are located in the upper “head space” section of the vessel, cover only a portion of the reaction vessel cross-section, and are therefore incapable of completely eliminating the above-mentioned problems. Some of such traditional slinger devices are disclosed in the prior art below.
U.S. Pat. No. 4,422,626 discloses an apparatus for building-up and repairing a refractory lining of an industrial furnace. The apparatus consisting of a rotary disc centrifugally throwing particulate refractory material against a portion of the lining to be repaired and comprising a horizontal row of hollow bolts with bores to spray water into an inlet conduit of annular cross section whereby the material passing through the conduit to the disc will be uniformly wetted.
WO2008036370 discloses a liquid-gas phase reactor system comprising a slinger secured to a drive shaft extending through at least a portion of an upper section of a reaction vessel and located below a first liquid inlet, wherein the slinger comprises an upper horizontal surface including a plurality of vertically raised vanes extending radially outward along a curved path.
A major shortcoming of the known slinger devices is that a large portion of the condensate is distributed only over a limited cross-section of the reaction vessel very little condensate actually reaching the reactor walls. Another shortcoming is that liquid tends to be distributed in large droplets rather than finely divided droplets. This results in solid carryover in the overhead condenser system and also solid deposition on the reactor wall. Consequently, such systems experience wall fouling, condenser plugging, and poor mixing of condensate with the liquid, phase reaction medium. Moreover, the known slinger devices are less effective at dissipating heat generated by the exothermic reactions. For example, with the exothermic oxidation of aromatic alkyls, much of the heat generated by the reaction is concentrated in the middle section of the liquid reaction medium. The hot spots can lead to undesired reactions, consumption of solvent and increased vapor generation; all of which contribute to higher operating costs and lower efficiency. Further, the uneven heating and cooling of the reaction vessel wall can produce thermal stresses at the vessel wall which can cause the shell leakage.
There is therefore felt a need to provide an improved slinger device for use in a multi-phase reactor system, which will overcome the afore-mentioned shortcomings of the known slinger devices by spreading the reflux (condensate) liquid uniformly about the inner walls of reaction vessel and optimizing the top reflux quantity as per the process requirements.